Disc substrate, method and apparatus for manufacturing same

ABSTRACT

A disc substrate of synthetic resin used for signal recording/reproduction by a head having a floating slider, in which the disc substrate is deburred to remove defects in appearance and is improved in strength and quality, and the manufacturing method and apparatus for the disc substrate. The manufacturing method includes a step of illuminating the laser light on at least the outer or inner rim portion of the disc substrate  2  of synthetic resin for transiently melting the illuminated portion. The manufacturing apparatus  1  includes a worktable  3  for supporting the disc substrate  2  in rotation, a positioning unit for positioning the disc substrate  2  at a pre-set position on the worktable  3  and a laser light source  4  for illuminating the laser light illuminating the laser light on the disc substrate  2  supported for rotation by the worktable  3 . On the outer rim of the disc substrate  2  is formed a raised portion  26  not larger than  15  μm in height. The raised portion  26  has a thickness larger than that of the outermost portion of the disc substrate  2.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a disc substrate of synthetic resinconstituting a disc operating as a recording medium for informationsignals, such as a magnetic disc, an optical disc or a magneto-opticaldisc, and a method and apparatus for manufacturing the disc substrate.More particularly, it relates to a disc substrate of synthetic resin inwhich a head is mounted on a floating slider, with the head and the discbeing arranged in close proximity to each other for realizinghigh-density recording/reproduction.

[0003] 2. Related Art

[0004] In a disc, such as an optical disc, magneto-optical disc or amagnetic disc, a disc substrate is used which is molded from a syntheticresin material exhibiting light transmitting performance, such aspolycarbonate resin. This disc substrate has an aperture at a midportion thereof.

[0005] Usually, disc substrates are manufactured by injection molding.That is, in manufacturing the substrates, a substrate material, usuallysynthetic resin, is melted on heating, and injected under elevatedpressure into a cavity corresponding in shape to the desired substrateshape. After cooling and curing of the substrate material, it is takenout from the cavity to manufacture the substrate of a desired shape.

[0006] Meanwhile, in usual injection molding, the inside of a metal moldis degassed.

[0007] However, since there are interstices in the outer and innerportions of the disc substrate molded in the metal mold, the resin ispulled by this degassing into these interstices to form burrs on theouter and inner portions. These burrs are extremely brittle and ready tobreak under the effect of various operations performed when taking outthe disc substrate out of the metal mold. That is, the disc substrate issignificantly lowered in strength in the outer and inner portionsthereof due to the burrs formed thereon.

[0008] Thus, the disc substrate molded by injection molding experiencesa problem that if, during transport of the disc substrate duringinspection or assembling steps, a hand area of a transporting jig of theouter rim clamp or outer and/or inner rim vacuum handling system iscontacted with the burrs on the outer and/or inner rims, these burrs aredetached and turned into projection-like defect of the magnetic filmthus lowering the quality of the disc substrate.

[0009] Moreover, if, after sputtering the magnetic layer on the discsubstrate formed of synthetic resin, pressure is applied to the outer orinner rims of the disc substrate, the burrs on these outer or innerrims, if present, are broken and cracked, thus causing exfoliation dueto absorbed or adsorbed water to lower the product quality.

[0010] The disc substrate formed of resin by injection molding suffersnot only from the burrs, but from the so-called honing phenomenon inwhich the disc substrate is reduced in thickness as the outermost rimthereof is approached, as shown in Fig. 1. In The hard disc, a floatinghead is floated by approximately 50 mm relative to the disc surface andis moved substantially radially of the disc. Since the outer rim portionof the disc is of increased recording area and hence the recording areais preferentially set to as close to the outermost rim of the disc forincreasing the recording capacity of the disc. Thus, the planar outerrim portion of the disc is desired for preventing the collision betweenthe disc and the floating slider. Therefore, a smaller magnitude of thehoning is desirable. In addition, from the convenience in designing thehard disc drive, this honing needs to be suppressed to within aprescribed magnitude. However, the honing tends to exceed the prescribedmagnitude if burrs are formed on the disc substrate.

SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to provide adisc substrate of synthetic resin which is deburred to eliminate defectsin appearance and which is of high quality with improved strength inouter and inner rims thereof.

[0012] In one aspect, the present invention provides a method formanufacturing a disc substrate including illuminating a laser light beamon at least the outer rim or the inner rim portions of a disc substrateof synthetic resin for at least transiently melting the illuminatedportion, in which the disc substrate is such a disc substrate used forsignal recording/reproduction by a head having a floating slider.

[0013] With the manufacturing method for the disc substrate according tothe present invention, the laser light is illuminated on at least theouter or inner rim of the disc substrate for transiently melting theilluminated portion so that burrs produced during molding are removed orare immobilized against accidental removal for improving the strength ofthe disc substrate.

[0014] In another aspect, the present invention provides a apparatus formanufacturing a disc substrate including a worktable adapted forsupporting a disc substrate and for being run in rotation, a positioningmember for positioning the disc substrate at a pre-set position on theworktable and a laser light source for being positioned by saidpositioning member and for subsequently illuminating the laser light onat least the outer or inner rim portions of the disc substrate supportedfor rotation by the worktable. The positioning member is preferablyinserted into a center opening in the disc substrate for positioning thedisc substrate.

[0015] In the above-described manufacturing apparatus for the discsubstrate according to the present invention, including the positioningmember for positioning the disc substrate on the worktable and the laserlight source for illuminating the laser light on the disc substrate, thelaser light can be illuminated on the appropriate positions on the discsubstrate, so that the burrs on the disc substrate formed during moldingcan be efficiently removed or immobilized to eliminate defects inappearance to improve strength of the disc substrate.

[0016] In yet another aspect, the present invention provides a discsubstrate of synthetic resin used for signal recording/reproduction by ahead having a floating slider, wherein the disc substrate has a raisedportion at an outer rim portion, with the thickness of the discsubstrate at the raised portion being thicker than the thickness of theoutermost rim of the disc substrate, with the raised portion being 15 μmor less in height.

[0017] With the above-described disc substrate of the present invention,having the raised portion on its outer rim portion, the disc substrateis increased in strength. The raised portion has a height not largerthan 15 μm, so that the honing may be comprised in the allowable rangein consideration of the fact that the floating head slider is caused torun radially of the disc from its outer rim portion towards itsrecording area.

[0018] With the manufacturing method for the disc substrate illuminatingthe laser light on at least the outer or inner rim portion of the discsubstrate 2 of synthetic resin for transiently melting the illuminatedportion, the material of the disc substrate illuminated by the laserlight beam is melted to remove burrs formed on the outer and/or innerrim portions of the disc substrate during injection molding so thatthere may be produced a disc substrate free of defects in appearance andwhich is also improved in quality and strength. With the manufacturingmethod for the disc substrate according to the present invention, thelaser light is preferably illuminated n the disc substrate surface at anangle of 30° to 45°, in which case the burrs can be removed moreefficiently and the disc substrate can be improved further in strength,while the yield in the manufacturing process may also be improved.

[0019] With the manufacturing apparatus for the disc substrate accordingto the present invention, the laser light can be illuminated on thecorrectly positioned disc substrate, thus enabling the burrs formedafter injection molding to be removed efficiently. Moreover, a discsubstrate may be provided which is freed of burrs and hence defects inappearance, and which is of high quality by being improved in strengthin the outer rim portion as a result of laser light illumination. Also,the production yield of the production process is improved by employingthe positioning mechanism capable of assuring correct positioning.

[0020] Also, the disc substrate of the present invention is improved instrength and superior in recording/reproducing characteristics becausethe thickness of the raised portion is within the allowable honingrange. In addition, the disc substrate manufactured by the manufacturingmethod and apparatus of the present invention is improved in strengthand moreover freed of burs so that it is of high quality and has nodefects in appearance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a cross-sectional view of a disc substrate forillustrating the honing.

[0022]FIG. 2 is a front view showing an example of a manufacturingapparatus for a disc substrate according to the present invention.

[0023]FIG. 3 is a cross-sectional view showing an example of amanufacturing apparatus for a disc substrate according to the presentinvention.

[0024]FIG. 4 is a schematic perspective view showing an example of amanufacturing apparatus for a disc substrate according to the presentinvention.

[0025]FIG. 5 is a cross-sectional view showing an example of a discsubstrate according to the present invention.

[0026]FIG. 6 is a first schematic view for illustrating the operation ofa manufacturing apparatus of the disc substrate according to the presentinvention.

[0027]FIG. 7 is a second schematic view for illustrating the operationof a manufacturing apparatus of the disc substrate according to thepresent invention.

[0028]FIG. 8 is a third schematic view for illustrating the operation ofa manufacturing apparatus of the disc substrate according to the presentinvention.

[0029]FIG. 9 is a fourth schematic view for illustrating the operationof a manufacturing apparatus of the disc substrate according to thepresent invention.

[0030]FIG. 10 is a fifth schematic view for illustrating the operationof a manufacturing apparatus of the disc substrate according to thepresent invention.

[0031]FIG. 11 is a sixth schematic view for illustrating the operationof a manufacturing apparatus of the disc substrate according to thepresent invention.

[0032]FIG. 12 is a seventh schematic view for illustrating the operationof a manufacturing apparatus of the disc substrate according to thepresent invention.

[0033]FIG. 13 is a schematic view for illustrating an example of apressing device used in an embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0034] Referring to the drawings, preferred embodiments of the presentinvention will be explained in detail.

[0035] The manufacturing apparatus for a disc substrate according to thepresent invention is designed for illuminating a laser light beam on adisc substrate of synthetic resin, and is configured as shown in FIGS. 2to 4. FIG. 2 is a front view of the manufacturing apparatus of the discsubstrate according to the present invention, FIG. 3 is across-sectional view taken along line A of the manufacturing apparatusshown in FIG. 2 and FIG. 4 is a perspective view showing essentialportions of the manufacturing apparatus.

[0036] The manufacturing apparatus 1 includes a worktable 3 forarranging and supporting a disc substrate 2, a positioning unit forsetting the disc substrate 2 at a pre-set position on the worktable 3, alaser light source 4 for illuminating a laser light beam on the discsubstrate 2, a base block for supporting the worktable 3 and a motor 5mounted at a portion of the base block for rotationally driving theworktable 3. The base block carrying the workable 3 and the motor 5 arearranged on a base plate 6.

[0037] The positioning unit is made up of a first positioning member 7for arranging and positioning the disc substrate 2 at a pre-set positionon the worktable 3 and for subsequently being detached from the discsubstrate 2 and a second positioning member 8 for being inserted into acenter aperture of the disc substrate 2 positioned by the firstpositioning member 7 and for subsequently being detached from the disc.

[0038] The base block includes a first base block member 9 forsupporting the worktable 3 and a second base block member 10 forsupporting the first base block member 9.

[0039] The worktable 3 is comprised of a column on the top of which isformed a protuberance having a center opening traversed by the firstpositioning member 7 and a slide shaft 17 adapted fro supporting thefirst positioning member. The worktable 3 also has a table surface 3a onthe upper end of the protuberance. It is on this table surface 3a thatthe disc substrate 2 is arranged and positioned.

[0040] The worktable 3 also has a portion of its outer rim supported bythe first base block member 9. The worktable 3 also has a bearing 11arranged in a recess on the contact surface thereof with the first baseblock member 9 and is rotated by a motor 5. At this time, the discsubstrate 2 is arranged on and supported by the worktable 3 so as to berotated in synchronism with the worktable 3.

[0041] The worktable 3 also has a disc suction opening 12 in the tablesurface 3a which is a protuberant surface contacted with the discsubstrate 2. This disc suction opening 12 is connected to an air suctionduct 13 in the worktable 3 and to an air sink vessel 14 opening in aportion of the contact surface with the first base block member 9. Thisair sink vessel 14 is connected to an air communication duct 15 and toan air suction opening 16. The disc substrate 2, arranged on the tablesurface 3 a, is sucked via disc suction opening 12, air suction duct 13,air sink vessel 14 and the air communication duct 15 to the air suctionopening 16 by an ejector, not shown, so as to be immobilized on thetable surface 3 a.

[0042] There are provided eight disc suction openings 12 in the surfaceof the disc substrate 2 for uniformly sucking the disc substrate 2. Itis noted that any optional number of the disc suction openings 12 may beprovided if these openings can suck the disc substrate 2 uniformly.

[0043] The air sink vessel 14 unifies the eight disc suction openings 12and the air suction duct 13 contiguous thereto into one to form aring-like structure. Consequently, this air sink vessel 14 can collectair streams form the eight disc suction openings 12 to form ahomogeneous air stream thus enabling the disc substrate 2 to be suckedby an ejector, not shown.

[0044] The positioning unit is made up of the first positioning member 7and the second positioning member 8, as described above.

[0045] The first positioning member 7 is mounted at an end of a slideshaft 17 and is adapted to be slid vertically of the disc substrate 2 bya cylinder, not shown. At this time, the slide shaft 17 is carried by alinear bushing 18 arranged in a portion of the outer rim of the shaft.This first positioning member 17 is adapted for transporting the discsubstrate 2 arranged on its surface, as will be explained subsequently,for arraying the transported disc substrate 2 at a pre-set position onthe worktable 3 for positioning the disc substrate 2. A linear bush stopring 19 is mounted on the upper end of the linear busing 18.

[0046] The second positioning member 8 is supported by a supportingbracket 20 mounted on a height adjustment shaft 21 . This heightadjustment shaft 21 has its side opposite to the side carrying thesupporting bracket 20 connected to a cylinder 40. Thus, the secondpositioning member 8 can be slid vertically of the surface of the discsubstrate 2. This second positioning member 8 is adapted forre-positioning the disc substrate 2 by being inserted into the centeraperture of the disc substrate 2 arranged at a pre-set position on thetable surface 3a by the first positioning member 7.

[0047] In articular, the positioning by the second positioning member 8is the re-positioning aimed at suppressing the offset of the discsubstrate 2 within the allowable range. This second positioning member 8permits more accurate positioning of the disc substrate 2 at the pe-setposition to enable the burs to be removed efficiently by illumination ofthe laser light. The positioning mechanism of these positioning memberswill be explained subsequently.

[0048] The base block is made up of the first base block member 9 andthe second base block member 10, as described above. The first baseblock member 9 is comprised of a column carrying a disk-shaped baseblock table section 22 and has a center opening 23 in which is insertedthe column of the worktable 3, as shown in FIG. 4. The base block tablesection 22 is adapted for directly supporting the worktable 3. The firstbase block member 9 has a bearing 11 on its inner lateral surfacecontacting with the worktable 3 for supporting the workable 3 adaptedfor being rotated about the slide shaft 17 as the center of rotation.Meanwhile, the first base block member 9 remains fixed at all times.

[0049] The first base block member 9 is provided with the aircommunication duct 1, connecting to the air sink vessel 14 arranged onthe worktable 3, for extending along the thickness of the first baseblock member 9 for being connected to the air suction opening 16 formedon the outer lateral surface of the first base block member 9. The discsubstrate 2 is sucked by this air communication duct 15 by the ejector,not shown, via the air sink vessel 14, air suction duct 13 and the discsuction opening 12.

[0050] The second base block member 10 is used for supporting the firstbase block member 9 in turn adapted for supporting the worktable 3. Thesecond base block member 10 has, in its surface contacted with the firstbase block member 9, a center opening 24 in which is inserted thecolumnar portion of the first base block member 9. The second base blockmember 10 also has its both lateral surfaces designed to cover portionsof the worktable 3 and the first base block member 9. On the lateralsurface of the second base block member 10 are mounted major portions ofthe motor 5. The motor 5 has its belt, not shown, connected to theworktable, and is adapted for rotationally driving the worktable 3.

[0051] The second base block member 10 need not be rectangular in shapeas shown in FIG. 4, but may be of any suitable shape if it can securethe worktable 3 and can enclose the belt of the motor 5. Thus, thesecond base block member 10 may be unified in structure with the firstbase block member 9. Moreover, the motor 5 may be positioned in the baseblock, that is, the belt of the motor 5, which drives the workable 3,may be enclosed in the base block.

[0052] The laser light source is preferably a CO₂ laser, but may be anyother suitable laser provided that it can machine the work without beingtransmitted through the transparent substrate and that it has anoscillation wavelength of the infrared range. If the substrate is nottransparent, it is possible to use other laser light sources. The laserlight source 4 is movable to permit adjustment of the angle ofillumination on the disc substrate 2 in a desired manner. Although thelaser light source 4 may itself be rotated instead of rotating the discsubstrate 2, it is more preferred for the laser light source 4 to beadjusted only with reference to the illuminating angle, as the discsubstrate is rotated, in consideration of the efficiency in themanufacturing process.

[0053] The laser light source 4 according to the present invention isadapted for being illuminated on the outer rim of the disc substrate 2for melting the material of the disc substrate and for partiallyvaporizing the melted material for removing the burrs formed on theouter rim of the disc substrate 2. In particular, for illuminating thelaser light to the outer rim of the disc substrate 2 from the laserlight source 4, the laser light is preferably illuminated at an angle of30° to 40° relative to the surface of the disc substrate 2.

[0054] In the vicinity of the portion of the disc substrate 2illuminated by the laser light from the laser light source 4 is arrangeda suction unit exemplified by a vacuum tube 25. This vacuum tube 25 isarranged for removing vaporization products yielded on melting andvaporization of the substrate material by illumination of the laserlight. This vacuum tube 25 is also movable freely. This vacuum tube isalso preferably arranged in the vicinity of the laser light source 4 soas to follow up with the laser light source 4. If the laser light source4 is designed to be of the rotatable type, as described above, thevacuum tube 25 may also be designed to be rotatable in keeping up withthe laser light source 4.

[0055] The laser light from the laser light source 4 may also beilluminated not only on the outer rim but also on the inner rim of thedisc substrate 2. This enables the burs formed on the inner rim of thedisc to be removed.

[0056] If the disc substrate 2, irradiated with the laser light from thelaser light source 4, has its outer rim irradiated with the laser light,there is formed a raised portion 26 on the outer rim of the discsubstrate 2, with the height h of the raised portion 26 being not largerthan 15 μm, as shown in FIG. 5.

[0057] It should be noted that the thickness of the disc substrate 2 inthe area thereof having the raised portion 26 is selected to be thickerthan the thickness of the outer most rim of the disc substrate 2 toavoid the situation in which the thickness of the outer most rim of thedisc substrate is thicker than that of the other portions, as shown inFIG. 1. The width of the raised portion 26 of the disc substrate 2 ispreferably not larger than 0.5 mm taking into account the area-matchingwith the recording area.

[0058] Moreover, the laser light is illuminated on the outer rim of thedisc substrate 2 for eliminating the burrs formed on the outer rim ofthe disc substrate. Also, by illuminating the laser light on the outerrim of the disc substrate, the burrs formed on the outer rim can beremoved. In addition, this thickness h can be suppressed so as to bewithin the tolerable range of honing desirable forrecording/reproduction. It is noted that, if the laser light isilluminated on the inner rim of the disc substrate 2, the burrs formedon the inner rim can be removed.

[0059] Meanwhile, even if the height h of the raised portion 16 exceeds15 μm, or if the burrs are not completely removed, the angle ofincidence of the laser light on the disc substrate 2 need not be 30° to45° provided that the operating condition is not such as to allow fordetachment of the disc substrate 2, that is that the operatingconditions are moderate.

[0060] Thus, the disc substrate 2, manufactured by the disc substratemanufacturing apparatus according to the present invention and themanufacturing method as later explained, is improved in strength becauseit is deburred or safeguarded against detachment, while in addition theraised portion 26 of a moderate thickness is formed on the outer rim ofthe disc substrate by radiating the laser light to the outer rim of thedisc substrate 2. Meanwhile, if the laser light is illuminated on bothsides of the disc substrate 2, the raised portion 26 is formed on eachside of the disc.

[0061] The method for manufacturing the disc substrate 2 using theabove-described manufacturing apparatus for the disc substrate ishereinafter explained. The manufacturing method for the disc substratehas the first positioning step, a second positioning step and a laserlight illuminating step.

[0062] In the first positioning step, the disc substrate 2 of syntheticresin molded by, for example, injection molding, is placed on the firstpositioning member 7, as shown in FIG. 6. At this time, the firstpositioning member 7 is projected upwards from the table surface 3a ofthe worktable 3. The first positioning member 7 supporting the discsubstrate 2 is moved in the direction of the worktable 3, that is in thedirection as indicated by arrow B in FIG. 6, as a result of movement ofthe slide shaft 17. It is noted that the slide shaft 17 is driven by thecylinder.

[0063] The result is that the disc substrate 2 is positioned on thetable surface 3a. The slide shaft 17 is moved further in the directionof arrow B as shown in FIG. 8.

[0064] The above-described process is the first positioning process.

[0065] Then, in the second positioning process, the second positioningmember 8 is moved towards the disc substrate 2 in the directionindicated by arrow C in FIG. 9. At this time, the second positioningmember 8 is supported by the supporting bracket 20 mounted on the heightadjustment shaft 21 so as to be moved by the cylinder, not shown, as adriving source.

[0066] The second positioning member 8 then is contacted with the discsubstrate 2 for re-positioning, as shown in FIG. 10. The disc substrate2 is sucked by an ejector, not shown, in the direction indicated byarrow A in FIG. 10 via the air suction opening 13, so as to beimmobilized in position.

[0067] The second positioning member 8 is then moved in the directionindicated by arrow D in FIG. 11 so as to be detached from the discsubstrate 2. This ultimately positions the disc substrate 2.

[0068] The above-described process ins the second positioning processwhich is the ultimate positioning process.

[0069] Finally, the laser light beam is illuminated on the outer rim ofthe disc substrate 2 from the laser light source 4 arranged in thevicinity of the manufacturing apparatus for the disc substrate 2, asshown in FIG. 12. If the laser light is illuminated on the outer rim ofthe disc substrate 2, the laser light is preferably illuminated so thatan angle 0 relative to the surface of the disc substrate 2 shown in FIG.12 will be 30° to 45°.

[0070] In the vicinity of a illuminating point of the laser light on thedisc substrate 2, illuminated on the disc substrate 2, there is arrangeda vacuum tube 25 adapted for sucking products yielded on evaporation ofthe material of the disc substrate 2 caused by illumination of the laserlight from the vacuum tube 25.

[0071] If the disc substrate 2, illuminated with the laser light at anangle of 30° to 45°, a raised portion 26 is formed on the outer rimtowards the outside of the disc substrate 2, as shown in FIG. 5, withthe height h of the raised portion 26 being not larger than 15 μm. Thethickness of the disc substrate 2 formed with the raised portion 26 isset so as to be thicker than that of the outermost area of the discsubstrate 2.

[0072] Moreover, since the material of the irradiated portion of thesubstrate is melted as result of illumination of the laser light, thedisc substrate 2 is deburred. Meanwhile, in the above-described firstand second positioning steps and in the laser light illuminatingprocess, the disc substrate 2 is sucked via the disc suction opening 12at all times.

[0073] Thus, the disc substrate 2, manufactured by the manufacturingmethod and apparatus for the disc substrate according to the presentinvention is deburred, presents no defect in appearance by beingsafeguarded against detachment, and has a moderate thickness at theouter rim when the laser light is illuminated thereon, so that it isimproved in strength and of high quality.

[0074] Meanwhile, it is only sufficient if the disc substrate 2 isformed of synthetic resin by injection molding and is usable as asubstrate for a disc used for recording information signals, such as amagnetic disc, an optical disc or a magneto-optical disc.

EXAMPLES

[0075] The present invention will be explained in detail with referenceto Examples based on specified experimental results.

Example 1

[0076] As a disc substrate of synthetic resin, fresh from the injectionmolding process, a burred disc substrate having a width from the outermost rim of 100 μm and a maximum thickness from the surface of the discsubstrate of 50 μm was prepared.

[0077] This disc substrate was illuminated by a laser light source underthe conditions of the laser spot diameters of 1.3 mm and 2.2 mm, the rpmof the disc of 30, 60, 90 and 120, the laser light illuminationintensity of 4.7 W to 12.6 W, the laser light illuminating timedurations of 1 sec and 2 sec and the illuminating angles θ of the laserlight beams of 30°, 45°, 65° and 90°.

[0078] The disc substrates, thus illuminated with the laser light, werechecked as to whether or not the disc substrate has been deburred, andresearches were conducted into illuminating conditions suitable fordeburring.

[0079] It was found that burs formed on the outer rim of the discsubstrate illuminated by the laser light were removed under conditionsof the laser spot diameters of 1.3 mm and 2.2 mm, the rpm of the disc of30, the laser light illumination intensity of 13.7×30/87 W to 13.7×80/87W, the laser light illuminating time durations of 2 sec and theilluminating angle θ of the laser light beams of 30° or 45°. The aboveconditions were used as the suitable illuminating conditions fordeburring.

[0080] Meanwhile, if the CO₂ laser is illuminated as described above,the irradiated portion by the laser light forms a raised portion aftermelting. This phenomenon has the effect of improving the intensity ofthe outer rim of the molded substrate. On the other hand, it may occurthat this protuberance exceeds the tolerable range for honing. There arealso occasions wherein the laser light is not illuminated in the rangeof burs under the effect of disc eccentricity such that burrs are left,or that, depending on the processing conditions, the melted portion ofthe laser light illumination sags to cause defects in appearance.

[0081] Thus, using an optical microscope, the range of conditions inwhich there is no burr or sag in the illuminated portion of the laserlight was identified and measurements were made of the width L of theraised portion after laser light irradiation and the maximum thickness hthereof using a contact type optical microscope for investigating intoan optimum condition of the laser light for deburring.

[0082] Table 1 shows the measurement results. For a disc substrate inwhich there is no burr or sag after laser light illumination and inwhich the thickness h of the raised portion is within the range of 15 μmwhen the allowable honing range is 15 μm, the width L and the maximumthickness h of the raised portion after laser light illumination areshown.

[0083] It may be said that, if measured values are not indicated inTable 1, burs are left or sag is produced or the maximum thickness h ofthe raised portion of the disc substrate exceeds 15 μm even after laserlight illumination. CO² laser working condition (t = 2 sec, m (commonvalue) = 30 rpm θ = 30°, d = φ1.3 mm θ = 45°, d = φ1.3 mm θ = 45°, d =φ2.2 mm size of raised tolerable tolerable tolerable power portion rangeoffset range offset range offset W h (μm) — — — — — — l (mm) — — — — — —W h (μm) — — — — 35960 — l (mm) — — — — 0.28-0.41 — V h (μm) 36071 —36082 — 36136 — l (mm) 0.45-0.56 0.11 0.33-0.48 0.15 0.23-0.30 0.07 V h(μm) — — 36013 — 36107 — l (mm) — — 0.37-0.45 0.08 0.20-0.24 0.04 V h(μm) — — 35949 — — — l (mm) — — 0.34-0.46 0.12 — — V h (μm) — — 36103 —— — l (mm) — — 0.22-0.22 0.11 — —

[0084] It is seen from the results of FIG. 1 that, for the laser lightilluminating angle ranging between 30° and 45°, burrs can be removed,while the thickness h of the raised portion of the melted portion can bereduced to 15 μm or less.

[0085] It is also seen that, with the laser spot diameter of 1.3 mm,disc rpm of 30, laser light illuminating time duration of 2 sec and thelaser light illuminating angle θ of 45°, the range of allowable valuesof the laser power and the amount of eccentricity that allow fordeburring and the thickness h of the raised portion 15 μm or less isbroad to render it possible to remove burrs more stably than under otherconditions.

[0086] It is also seen that, if the illuminating angle θ is 30°, theoptimum range of the laser power is narrow, however, the raised portioncan be reduced in thickness.

Example 2

[0087] Researches were then conducted into changes in intensity byirradiation of the laser light.

[0088] First, as disc substrates fresh from the injection molding, discsubstrates having burrs similar to those n Example 1 were prepared.

[0089] Of the above disc substrates, a disc substrate S-1 illuminated bythe laser light and a disc substrate S-2 not illuminated by the laserlight were prepared. By way of laser light illuminating conditions, thelaser spot diameters, disc rpm, laser power representing the laser spot,laser light illuminating time duration and the laser light illuminatingangle θ were set to 1.3 mm, 30 rpm, 7.7 W, 2 sec and 45°,

[0090] The disc substrate S-1, illuminated by the laser light under theabove conditions, was deburred, with the maximum thickness of the raisedportion being 15 μm.

[0091] Of the disc substrate S-1 illuminated by the laser light and thedisc substrate S-2 not illuminated by the laser light, the strength ofthe disc substrates was measured, after sputtering a magnetic film bythe following method:

[0092] Using the pressing device 30 shown in FIG. 13, the discsubstrates 2 were arranged in a cassette 31 and held at two points 32 a,32 b. Using a tension gauge, the disc substrates were pressed by 100 gf.After the pressing at 100 gf was continued for 10 sec, the discsubstrates 2 were checked as to the absence of cracks or bursts. Thepressure was similarly increased and maintained for the same timeduration in order to check that the disc substrates were free of cracksor bursts.

[0093] The pressing was discontinued at a time point cracks or burstswere noticed. The pressure prevailing at this time was defined as thestrength of the disc substrate.

[0094] The above results are shown in table 2. TABLE 2 number of timesof tests S-1 S-2 first  900 gf 100 gf second 2000 gf 100 gf

[0095] It is seen from Table 2 that, with the disc substrate S-1illuminated by the laser light beam, cracks were noticed at 900 gf andat 2000 gf for the first and second measurements, respectively. On theother hand, with the disc substrate S-2 not illuminated by the laserlight, cracks were noticed at 100 gf for Dotn the first and secondmeasurements.

[0096] It is seen from this that raised portions were noticed on theouter rim of a disc substrate illuminated by the laser light at theouter rim in particular, and that this raised portion contributed toincreased strength.

[0097] Although the disc substrates S-1 and S-2 showed a wide differencein the pressure magnitudes for the first and second measurements, thisdifference is thought to be an error insignificant as compared to thedisc substrate S-2 not illuminated by the laser light.

What is claimed is:
 1. A method for manufacturing a disc substratecomprising the step of: illuminating a laser light beam on at least theouter rim or the inner rim portions of a disc substrate of syntheticresin for at least transiently melting the illuminated portion said discsubstrate being such a disc substrate used for signalrecording/reproduction by a head having a floating slider.
 2. Themanufacturing method as claimed in claim 1 wherein the laser light beamis illuminated at an angle of 30° to 45° relative to the surface of saiddisc substrate.
 3. The manufacturing method as claimed in claim 1wherein the laser light beam is illuminated on the outer rim portion ofthe disc substrate for forming a raised portion 15 μm or less in heighton the outer rim portion of the disc substrate.
 4. An apparatus formanufacturing a disc substrate comprising: a worktable adapted forsupporting a disc substrate and for being run in rotation; a positioningmember for positioning the disc substrate at a pre-set position on theworktable; and a laser light source for being positioned by saidpositioning member and for subsequently illuminating the laser light onat least the outer or inner rim portions of the disc substrate supportedfor rotation by said worktable.
 5. The apparatus for manufacturing thedisc substrate as claimed in claim 4 wherein the positioning member isinserted in a center opening formed in the disc substrate forpositioning the disc substrate.
 6. The apparatus for manufacturing thedisc substrate as claimed in claim 4 wherein the laser light sourceilluminates the laser light at an angle of 30° to 45° on the surface ofthe disc substrate.
 7. The apparatus for manufacturing the discsubstrate as claimed in claim 4 wherein the worktable has a disc suctionopening for sucking and immobilizing the disc substrate.
 8. Theapparatus for manufacturing the disc substrate as claimed in claim 4further comprising: suction means for sucking a product formed onevaporation of the material of the disc substrate as a result ofillumination of the laser light.
 9. The apparatus for manufacturing thedisc substrate as claimed in claim 4 wherein the laser light sourceilluminates the laser light on the outer rim portion of the discsubstrate for forming a raised portion 15 μm or less in height on theouter rim portion of the disc substrate.
 10. A disc substrate ofsynthetic resin used for signal recording/reproduction by a head havinga floating slider, wherein the disc substrate has a raised portion at anouter rim portion, with the thickness of the disc substrate at theraised portion being thicker than the thickness of the outermost rim ofthe disc substrate, with the raised portion being 15 μm or less inheight.